Induction heating apparatus



1958 J. w. PEACH EI'AL 2,353,404

INDUCTIQN HEATING APPARATUS.

Filed April 18, 1957 INVENTORS James W. Peach 8- Cldrence A.Kuhne StatesINDUCTION HEATING APPARATUS Application April 18, 1957, Serial No.653,594

7 Claims. (Cl. 219--10.49)

This invention relates to electric induction furnaces and moreparticularly to furnaces which can be used for heating billets, bars andsimilar workpieces to forging or extruding temperatures.

In the heating of workpieces for forging or extrusion by automatizedapparatus, the advantages of using electrical induction apparatuscapable of heating the workpiece rapidly, successively and accurately toa predetermined temperature is well recognized. In induction coil billetheating apparatus it is usual to position the billet centrally of theinduction coil and to shift the billet longi- .tudinally through atunnel formed by the convolutions of the induction coil. In order tokeep the power factor of the induction coil reasonably near unity, it isdesirable to keep the air gap between the workpiece and the convolutionsof the induction coil as small as possible.

In conflict with the foregoing desideratum is the necessity of providingthermal and electrical insulation between the workpiece pathway and theconvolutions of the induction coil. An accepted practice in the art hasbeen to provide metal or ceramic liners of heat resistant materialsurrounding the workpiece pathway to protect the induction coils fromheat radiated by the workpieces and from physical injury which might becaused by insertion or withdrawal of heavy workpieces from the coil. Inaddition to providing thermal and physical protection for the inductioncoil, the liner structure should be sufiiciently strong, rigid andrugged to support the workpieces during the heating cycle.

It is further desirable in such furnaces to provide wear rails extendinglongitudinally inside the induction coil along which rails theworkpieces may be shifted. At forging temperatures of about 2000 F. andabove, workpiece supporting rails of known alloys have very littlestrength in bending so that even though rail supports are provided everyfew inches, heavy and thick rails arerequired to support the mass of theworkpiece. The allowance of additional space for heavy railsnecessitates an even greater air gap between the induction coil and themetal to be heated. The excessive air gap tends to result in lowefficiency of the induction heating coil and a low power factor of thecoil so that an excessive number of capacitors are required in order tocorrect the power factor to a predetermined figure.

In the heating of workpieces for forging, it is imperative that theworkpieces be heated throughout to a relatively uniform temperature sothat no cold areas or temperature differentials will exist betweendiiferent portions of the heated workpiece. This requirement becomesincreasingly important in automatized apparatus wherein the heatedworkpiece is delivered to the forging presses almost immediately afterbeing ejected from the induction heating furnace. In such apparatus thedwell time after heating, before the billet is delivered to the forgingpress, may be so short that temperature equalization of the differentportions of the'billet is not obtainable. Thus, it is necessary that theworkpiece support surfaces or atent rails within the induction furnacebe adapted for operation at relatively high temperatures so that areasof a workpiece in contact therewith will not be unnecessarily cooled byconduction of heat to the workpiece support members.

Accordingly, it is an object of this invention to provide a furnacehaving improved workpiece supporting surfaces.

It is another object of the invention to provide a hollow liner forbillet heating furnaces with elongated support rails carried within theliner for slidingly supporting workpieces and with such rails beingsupported in a manner such that they are maintained at a firstrelatively high temperature while the members which support the railsare maintained at a second and relatively low temperature.

it is a further object of the inventionto provide a workpiece supportingrail-which is maintained at a first temperature and to provide a loadsupporting member for imparting strength and rigidity to the rail, withthe latter member being maintained at a relatively low temperature andwith the assembly having a high impedance to transverse heat flowbetween the workpiece contacting member induction coil assemblyincluding the workpieces supported within the coil liner.

It is still another object of the invention to provide an induction coilassembly constructed so as to permit removal and replacement of theworkpiece supporting rails without disturbing the induction coils andthe induction coil liner.

It is a still further object of the invention to provide an improvedheat resistant workpiece supporting rail having a head portion alongwhich workpieces may slide and having a strength imparting base portionparallel thereto with the head portion and the base portion beingthermally insulated from each other so as to present a high impedance totransverse heat flow from workpieces supported thereon.

It is a still additional object of the invention to provide an inductionheating coil having a plurality of longitudinally positioned workpiecesupport members which are thermally insulated from the induction coil sothat the support members will conduct a limited amount of heat from thesurface of a workpiece.

It is a still different object of the invention to provide a rigid,rugged and compact induction furnace chamber capableof supporting largeand cumbersome billets or workpieces and operative to heatsuchworkpieces uniformly to predetermined temperatures.

These and other objects of my invention will be apparent from thefollowing description taken in accordance with the accompanying drawingthroughout which like referencecharacters indicate like parts, whichdrawing forms a part of this-application and in which:

Figure 1 is a longitudinal side view of an electrical induction heatingfurnace in accordance with the invention;

Fig. 2 is a sectional view taken along the linesII-II of Fig. 1 andillustrating the induction coil liner member and the workpiecesupporting rails and insulating structure; and

Fig. 3 is a sectional view similar to that of Fig. 2,

showing a second embodiment of our invention and illustrating analternative structural arrangement of the workpiece supporting rails andthermal insulating means.

In copending application Serial No. 630,367, filed December 24, 1956,and assigned to the assignee of the present application there isdisclosed an induction furnace apparatus which is in many respectssimilar to the induction furnace of the present invention and whichdiscloses a type of high speed production apparatus in which the presentinvention may be advantageously employed.

Referring now to the drawings, the induction heating apparatus as shownin Fig. 1 comprises a plurality of coil sections formed of a singlelayer of a hollow rectangular electrical conductor 12 with said sectionsbeing arranged in end to end relationship so as to provide a workpiecepathway 14 or tunnel axially therethrough. The furnace coil assembly 16is preferably mounted horizontally and longitudinally on top of anappropriate table or support frame (not shown) and is supported abovethe table surface by means of a pair of end plates 18 which arepositioned at opposite ends of the end-to-end aligned sections ltl. Theend plates 18 are preferably of substantially rectangular configurationand are provided with substantially rectangular openings through whichthe ends of an induction coil liner member 20 project. The two end platemembers 18 thus support each end of the liner member 2%, and theconvolutions 12 of the'induction coil 10 are carried on and supported bythe liner member 2% intermediately of the end plate members 18. Thehelical convolutions 12 of the induction coil 10 may be insulated fromeach other and from the coil liner member 2a by means of glass clothsleeving and glass tape impregnated with a suitable high temperaturevarnish or other suitable insulation imposed between adjacentconvolutions of the coil. The ends 22 of each section 10 of theinduction coil are bent outwardly and may be provided with appropriateelectrical connections and connections for a water cooling conduit forcirculat ing a coolant through the convolutions 12 of the coil. Thestructural details of the induction coil convolutions, the electricalconnections and water connections are essentially conventional and havebeen omitted from the drawing. The induction coil sections 10 preferablyextend over the entire space between the end support plate members 18.In the form of the invention illustrated in Fig. 1, the inductor coilsections 10 are shown as being formed of a hollow rectangular conductivemember although it is to be understood that the coil sections may beformed of circular tubing or of a hollow conductor having another formof cross section.

The coil liner member 20 on which the coil sections 10 are supported ispreferably formed of a thin sheet of a tough, wear resistant, heatresistant and non-magnetic metal of relatively low electricalconductivity. The thin metal sheet is bent to form an elongated hollowsubstantially rectangular tube 26 having rounded corners and havingexternal dimensions slightly larger than the internal dimensions of theinductor coils 10 with the internal dimensions of the liner member 20being sufficiently larger than the external dimensions of the workpiecesto be heated so as to accommodate appropriate insulation and specificworkpiece supporting means to be hereafter described.

As shown in Fig. 2, the liner member 20 is split longitudinally at onepoint in its periphery so as to provide a longitudinally extendingopening 24 which interrupts the peripheral continuity of the linermember 20. This interruption or longitudinal opening 24- in the linermember 20 is'pr'ovided to prohibit the induction coils from inducinga-circulating current in the liner member 20 which would reduce theefficiency of the apparatus and would tend to overheat the liner member20.

The metal of which'the liner member 20 is formed may be, for example, ahigh tensile strength stainless steel or nickel alloy steel havingsubstantially non-magnetic properties so that the magnetic field inducedby the induction coil will pass transversely through the coil linermember 20 to thread through the workpieces positioned in the workpiecepathway 14. The longitudinal opening 24 in the stainless steel linermember 20 may if so desired be sealed by means of two layers of asbestossheet and appropriate clamping means (not shown) on opposite sides ofthe liner member 20 adjacent the longitudinal opening 24. Such sealingmay be particularly desirable when the workpieces are to be heated in aninert atmosphere. With the sealing arrangement described and theimperforate coil liner member 20, the inert atmosphere may besubstantially contained within the coil liner 20 thereby rendering itunnecessary to provide an additional enclosure for containing the inertatmosphere. In addition, the asbestos seal of the longitudinal opening24 as described is operative to prevent hot gases and combustionproducts from the heated workpiece from contacting the induction coilinsulation.

If so desired, the induction furnace assembly 16 may be provided withelongated tension members extending between the end plates forresiliently holding the coil sections in tightly pressed end to endalignment, thereby suppressing vibration of the coil sections.Alternatively, the coil sections may be held against vibration by springloaded jack screws (not shown) used to force apart two flat washers ofnonmagnetic material having external dimensions larger than the coil lband having inside dimensions slightly larger than the liner member. Byforcing the washers longitudinally apart the coil sections ll arecompressed against the opposite end plates 18 and are thereby restrainedagainst vibration and electromagnetic forces. The restraining washersare preferably split at one point adjacent the liner periphery toprohibit circulating currents from flowing in the washer.

As best shown in Fig. 2, the coil liner member 20 is positionedlongitudinally within the aligned coil sections 10 and is equally spacedfrom the inner walls 26 of the coil convolutions. On the exterior of thecoil liner member 20 there is provided a thin sheet 28 of thermallyconductive metal which may be fastened to the coil liner member by meansof conventional screw type fastening member. The thermally conductivesheetZS carries'on the outside thereof a plurality of fiuidconduitmembers 30 which extend longitudinally of the coil linerand areinterconnected at their ends so as to provide a serpentine path for acooling fluid. The serpentine cooling fluid conduit 30 is provided toabsorb heat which vis conducted from the heated workpiece to the linermember 29 to thereby maintain the coil liner member 29 relatively coolso that it will have maximum, strength for supporting the workpieces. Insome applications of the present invention the coil liner 2% may besufficiently cooled by means of the fluid cooled induction coilconvolutions 12 in combination with appropriate thermal insulatingmaterial 32 positioned adjacent the inside of the coil liner member 20.In such cases the serpentine cooling fluid conduit 36 may be dispensedwith so that the coil convolutions It may be carried closely adjacentthe exterior of the coil liner member 20, thus providing a furnace inwhich the air gap between the coil sections 10 and the workpieces isminimized. Closely adjacent the inside of the coil liner member 20 thereis provided the relatively thick layer 32 of thermal insulating materialwhich may, for example, be a high temperature insulating material suchas aluminum silicate felt. Inside the layer of thermal insulatingmaterial 32 there is provided an inner liner 34 of high temperaturealloy material in the form of a thin sheet. This inner liner 34 isprovided to hold the thermal insulating material 32 in place closelyadjacent the liner member 20 and to protect the insulating material 32from deterioration or damage caused by combustion products, scale orother extraneous material which may be introduced by the workpieces. Theinner liner 34 is supported in position by short bolts 36 formed of heatresistant material which extend through the inner liner 34, the

thermal insulating material 32 and are threaded into or otherwiseattached to the coil liner member 20. The inner liner member 24 may ifso desired be perforated or saw cut to prevent deformation thereof dueto heat expansion. Alternatively the inner liner 34 may, if so desired,be formed of heat resistant wire screen or of short sections of heatresistant alloy with the construction in either case being designed toavoid bowing or deformation of the liner 34 when heated. At angularlyspaced positions inside the inner liner 34 and contiguously adjacent theworkpiece pathway 14 there are provided a plurality of longitudinallyextending rail members 40 positioned and adapted to support workpiecesin the work piece pathway 14. The mail members 40 preferably extendcontinuously from one end of the furnace liner 20 to the other end andthereby provide a smooth and continuous surface along which theworkpieces may be shifted or slid.

Between each rail member 40 and the inside of the liner member 20 thereis provided a pair of spaced, longitudinally extending rods 42 forsupporting the rail member 40 in parallel spaced relation to the linermember 20. The load supporting rods 42 may be held in position byappropriate lugs attached to the liner member 20 at spaced pointstherealong or may be otherwise fastened relative to the liner 20 so asto permit longitudinal expansion of the rods. The load supporting rods42 are effective to rigidly support the rail member 40 along its fulllength so that the rail member 40 will not tend to be deflected or bentby heavy loads positioned thereon when the rail member is heated totemperatures approaching the workpiece temperatures. At forgingtemperatures of about 2000" F. and above, workpiece supporting railmembers of known heat resistant alloys have very little strength inbending so that even though separate rail support pillars were providedevery few inches, a heavy rail of undesirable thickness would berequired to adequately support the load. Furthermore, use of theinsulating material 32 as the sole supporting means for the rails isgenerally inadequate in that heavy billets will tend to compress theinsulating felt 32 after a short period of use, thereby reducing theinsulating effect and necessitating complete dismantling of the heatingfurnace for replacement of the thermal insulating material.

As shown in Fig. 2, the rail members may be located in position by aremovable attachment to the inner liner member 34. The rail 40 is boltedat the infeed end to prevent movement with the billets, and is laterallypositioned by lugs welded to the inner liner at spaced positionstherealong. The weight of the rail members 40 and the workpiecepositioned thereon is supported by the cylindrical rods 42 which arepositioned between the rails 40 and the coil liner member 20. Thecylindrical load supporting rods 42 preferably extend the full length ofthe induction heating furnace 116 so that the rail 4i? is sup ported bythe rods 42 at all points along its full length with the load-carryingrods 42 in turn being supported by the coil liner member 20. By virtueof the heretofore described rail support construction, it is possible toemploy a work supporting rail member 40 having a relatively smallthickness as compared to its Width. The use of such a thin rail is adistinct advantage in that thicker rails have a tendency to bow ordeform due to temperature differential between the inside and outsidesurfaces of the rail. Experimentation has shown that excessively thickrails tend to fracture after extended periods of use because of thethermal stresses created within such thicker rails. In addition, the useof the thin work supporting rail members 40 as heretofore describedpermits a much smaller distance between the workpiece and the coil turns12 thus permitting a much smaller air gap. The workpiece supportingassembly formed by the rail member 40,

inner liner 34 and support rods 42 is not permanentlyjoined to the coilliner member 20. Rather, each rail assembly is releasably secured to theliner member by fiat headed bolts of heat resistant material whichextend through the rail, through appropriate openings in insulatingmaterial 32, and are threaded into or otherwise fastened to the linermember 20 so as to maintain the rod members 42 in resiliently pressedtangential engagement with the liner member 20. By use of thisreleasable attachment of the rail assemblies within the furnace a systemis provided in which any one of the rail assemblies may be individuallyremoved from the furnace without disturbing the liner member 20 or theinsulating material 32. This enables replacement of any worn or damagedrail member simply by removing the bolts which independently connect itto the liner member 20.

In Fig. 3 there is shown an alternative structural arrangement in whicha compound rail structure 44 includes a channel member 48, a layer ofthermal insulating material 5i) and a work supporting rail member 40. Inthe apparatus of Fig. 3 the induction coil sections 10, the coil linermember 20, the thermal insulating material 32 and the inner liner 34 areessentially similar to those same components as shown in Fig. 2 and are,therefore, designated by the same numerals as in Fig. 2 In Fig. 3 theload supporting rod members 46 comprise longitudinally extending hollowtubular members which may be provided with appropriate end connectionsfor circulation of a cooling fluid therethrough. The load supportingtubes 46 may be attached to the liner member 20 by bolts or byappropriate clamps threading into or otherwise making positiveattachment to liner member 20. On the interior side of the loadsupporting tubes there is provided a longitudinally extending channelmember 48 formed of heat resistant alloy and attached to the loadsupporting tubes 46 by welding at spaced positions therealong. Thechannel member 48 is formed and adapted to retain within its channel aceramic or firebrick thermal insulating material 50 which extendslongitudinally from end to end of the channel member 48. The workpiececontacting rail members 40 are similar to the rail members 40 as shownand described with reference to Fig. 2. The rail members 40 provide alongitudinally extending, smooth and continuous surface along whichworkpieces may be shifted. The rail member 40 may be secured to thechannel member 48 by means of appropriate flat headed bolts (not shown)extending through the rail 40, through the thermal insulating material32 and threaded into or otherwise fastened to the liner member 20. Byusing the weight carrying metal liner 20 and the relatively thincompound rail members 44 the inevitable air gap between the coil andworkpieces can be made appreciably smaller than that of prior artfurnaces. Likewise, reduction of the spacing between the workpieces andthe induction heating coils 10 aifords a more compact furnace than thatof prior art induction heating apparatus. By providing the thermalinsulating material 50 between each channel member 48 and each railmember 40, a compound rail structure 44 is provided which has a highimpedance to transverse heat flow from the rail member 40 to therelatively cold liner member 20. By means of the unique rail structureof the invention, the coil liner member 20 is maintained relatively coolfor maximum strength, thereby enabling it to be employed as a loadcarrying member and thus eliminating the necessity of providing supportmembers extending through the coil liner 20 and between convolutions ofthe induction coil as has been common in the prior art.

Throughout the specification the term induction heating coil has beenused to apply to the electromagnetic inducing element relative to whichthe workpiece is positioned to be heated by electromagnetic induction.The term heating coil is to be broadly construed to includeelectromagnetic inductor devices of all types regardless of whether theinductor coil assembly is substantially circular in cross section or issubstantially rectangular in.

The term rail is to be construed as meaning any in tegral orsectionalized surface on which a billet or the like may slide. Likewise,whereas the invention has been shown and described asrelating to anapparatus for heating' substantially-rectangular workpieces, it is to beunderstood that it is equally applicable to similar apparatus forheating cylindrical workpieces or workpieces having other specialcross-sectional configurations.

While'the present'invention has been shown-in one form only, it will beobvious to those skilled in the 'art that it is not solimited but issusceptible of various other changes and modifications without departingfrom the spirit and scope thereof.

We claim as'our invention:

1. An induction heating apparatus comprising an induction coil having aworkpiece pathway extending'l itudinally therethrough, a liner memberfor said coil cone prising a-thin-walled metal tube of interruptedcircumferential continuity, means for supporting said liner memberadjacent each end-thereof with said coil being externally supported bysaid liner member, a plurality of work supporting rails angularly spacedand longitudinally extending within said liner member adjacent saidpathway, and a plurality of rail support members positioned between saidrails and said liner member so as to rigidly support said rails withsaid rails being thennally insulated from said liner member so as tosubstantially restrict the flow of heat from said rails to said linermember.

2. An induction heating apparatus comprising'an induction coil having aworkpiece pathway extending longitudinallytherethrough, a'liner memberfor said coil comprising a thin-walled metal tube of interruptedcircumferential continuity, means for supporting said liner memberadjacent each end'thereof with said coil being externally supported bysaid liner member, a plurality of work supporting rails angularly spacedand longitudinally extending within said liner member adjacent saidpathway, a plurality of rail support members positioned between saidrails and said liner member so as to rigidly support said rails withsaid rails being thermally insulated from said liner member so as tosubstantially restrict the flow of'heatfrom said rails to said linermember, and means for cooling said liner member so that said linermember may be maintained at a temperature at which it retainssubstantial mechanical rigidity.

3. In apparatus for induction heating having a longitudinally extendingworkpiece pathway, a thin-walled metal tubular member of interruptedcircumferential continuity-surrounding said pathway, means forsupporting said member adjacent the ends thereof, an induction coilcomprising a plurality of convolutions of electrical conductorsupportedon theoutside of said tubular member, a plurality of longitudinallycontinuous workpiece supporting rails supported contiguous to saidpathway by said tubular -member, each of said rails comprising afacing'member along which workpieces may be slid, a load supportingmember adapted to be positioned longitudinallyadjacent the inside ofsaid tubular member, and thermal insulating means disposed between saidfacing member and said load supporting member so as to substantiallyresist the flow of heat from said workpieces to said load-supportingmember.

4. An induction heating coil having longitudinal work supporting railswithin the coil, a thin walled metallic linermember positionedlbetweensaid coil and said rails for supporting'the same,'fiui'd conduit meansthermally associated with said liner member for cooling the same, andelongated rail support members positioned in parallel adjacency betweensaid rails and said liner member 10 sunlort said rails, with said railsand rail support members being connected to said'liner so as to have ahigh impedance to transverse heat flow whereby said supports conduct arelatively small amount of heat from said rails and the'heated surfaceof a workpiece con- :1 ans to said rails.

.1. An electric heating furnace comprising aninductiou heating coil,workpiece guide rails within said coil, 21 thin-walled metal linermember outside the rails Within the coil, a plurality of elongated railsupportmembers positioned longitudinally of said coilbetween said railsand said liner member so as to support said rails in parallel spacedrelation to said liner member, with said support members being formed ofa material of low heat conductivity and having a small contact area withsaid liner member so as to provide a high impedance to heat flow fromsaid rails to said liner member.

6. In an induction furnace a substantially tubular heating coil, athin-walled liner member of interrupted circumferential continuitywithin and adjacent said coil, means at the ends only of said linermember for supporting same, heat resistant longitudinally continuousmetal rails positioned within and spaced from said'liner member, andrail support members longitudinally positioned within said coil betweeneach of said rails and said liner member, said rail support membersbeing in the form of substantially cylindrical rods and being adapted totangentially engage both said liner member and said rails to provide aheat conduction path thereetween, with said path having a substantiallyreduced cross-sectional area portion.

7. An induction heating apparatus comprising a heating coil, anelongated hollow liner member longitudinally positioned within said coiland supporting said coil, a plurality of longitudinally and angularlyspaced support members within said liner member, releasable means forattaching said members to the interior of said liner member, a pluralityof longitudinally continuous workpiece contacting rails secured to saidsupport members, with each of said rails and its associated supportmembers comprising a workpiece supporting assembly independentlyremovable from said liner member upon release of said releasable means.

References Cited in the file of this patent UNITED STATES PATENTS2,365,021 Strickland Dec. 12, 1944 2,676,234 Lackner et al. Apr. 20,1954 2,716,695 Cutliff et al. Aug. 30, 1955 2,780,706 Brogan Feb. 5,1957

